The effect of layer thickness on the density, microstructure and mechanical properties of ti-5al-2.5 Sn (Ti-Al-Sn) titanium alloy was studied. The results show that with the decrease of thickness, the energy density of the laser body will be increased, and the Ti-Al-Sn alloy sample with a density greater than 99.0% can be produced when the layer thickness reaches 60 mu m.Using SLM technology of Ti-Al-Sn alloys mainly includes three kinds of microstructure, the needle alpha′ martensite structure respectively, needle alpha′ martensite + island shape alpha m mixed groups and the pure form of alpha m group. As the thickness of the layer increases and the scanning rate slows down, the cooling rate of the sample decreases gradually. When the thickness of the layer was increased, the mechanical properties of the ti-al-sn samples were reduced. The Ti-Al-Sn samples obtained at different layers were characterized by ductile fracture at room temperature.